Investigating micropollutant removal in sustainable biological wastewater systems

Abstract

Annually, over 300 million tonnes of chemicals used globally from human activities find their way into the aquatic environment via poorly treated wastewater in high income countries (HICs) and partially/untreated wastewater in low-middle income countries (LMICs). Some of these chemicals have been shown to have significant adverse effects on wildlife and potentially humans, hence, legislative environmental quality standards are being considered in the EU and other developed countries. This issue comes at a time when increasing energy costs are driving water companies towards sustainable treatment options – which would run counter to the use of energy intensive tertiary treatment systems that have been advocated for effective micropollutant removal. Hence, this project looked into the effectiveness of low-energy systems such as up-flow anaerobic sludge blanket reactors (UASBs) and passive-energy waste stabilization ponds (WSPs) in comparison to the high-energy activated sludge systems to remove different classes of micropollutants including industrial chemicals (PAHs and PBDEs), personal care product (triclosan), and steroidal hormones (E1, E2, E3 and EE2). Effective analytical methods to measure the micropollutants were developed and validated (method detection limits ranging from 0.2 – 10.8 ng/L), and used to determine the occurrence and levels of the selected contaminants in UK and Brazil municipal wastewater. The observed levels of these chemicals were similar between both countries and those reported in literature- thereby indicating the prevalence of these chemicals in both LMICs and HICs. Wastewater treatment plant studies indicated that the passive-energy WSP was more effective (89 – 99 %) in removing all the classes of chemicals when compared to the energy-intensive activated sludge system (74 – 94 %) and low-energy UASB system (88 – 93 %). The removal of these micropollutants in WWTPs was mainly due to biodegradation and sorption, while photo-degradation (in WSP) and volatilization also contributed. The experimentally determined first-order degradation rates showed that under aerobic conditions, the degradation of the different groups of chemicals was significantly different, with estrogens degrading the fastest (0.1129 h-1 with activated sludge inocula) and high molecular weight PAHs the slowest (0.0033 h-1); while no degradation was observed under anaerobic conditions for any of the studied contaminants. Furthermore, the predicted and measured effluent concentrations indicated that effluent from the studied WWTPs poses a risk when discharged into receiving waters- as the concentrations of some chemicals were above recommended environmental quality standards (EQS), though, river dilution might ensure compliance.